1. Field of the Invention
The present invention relates to a gas treatment apparatus for gelatinizing a coated film coated on the front surface of a substrate and forming an insulation film, the coated film being formed by dispersing particles or colloid of a start substance of a film component to solvent.
2. Description of the Related Art
As methods for forming an inter-layer insulation film of a semiconductor device, CVD method, heat oxidizing method, and so forth are known. In addition, sol-gel method is known. In the sol-gel method, a coating solution of which colloid of TEOS (tetraethoxysilane: Si(C.sub.2 H.sub.5 O).sub.4) is dispersed to organic solvent such as ethanol solution is coated on the front surface of a semiconductor wafer (hereinafter simply referred to as wafer). The coated film is gelatinized and dried. Thus, a silicon oxide film is obtained. An example of such a method has been disclosed in Japanese Patent Laid-Open Publication Nos. 8-162450 and 8-59362.
FIGS. 9A, 9B, and 9C show degeneration of a coated film in such a method.
When a coating solution is coated on a wafer, particles or colloid 100 of TEOS is dispersed to solvent 200 (refer to FIG. 9A). Thereafter, the coated film is exposed to alkaline atmosphere or heated. Thus, since TEOS is polycondensated and hydrolyzed, the coated film is gelatinized and thereby a mesh structure of TEOS 300 is formed (refer to FIG. 9B). The solvent of the coated film is substituted with another solvent 400 such as acetone so as to remove moisture from the coating solution (refer to FIG. 9C). The solvent substituting treatment is a hydrophobic treatment for the film. In other words, since an OH radical tends to absorb moisture, when the film is reacted with for example HMDS, the OH radical bound to an edge portion of Si--O coupling is substituted with another organic substance.
After the coating solution is dried, a coated film of silicon oxide film is obtained. Moreover, in the solvent substituting treatment shown in FIG. 9C, solvent whose surface tension is smaller than that of ethanol is used. Thus, when the solvent vaporizes, since large stress is not applied to the mesh structure of TEOS, the film can be prevented from breaking.
The silicon oxide film formed by the sol-gel method has many air pores. Thus, the dielectric constant .di-elect cons. of the oxide film is very close to that of vacuum. Consequently, the electric resistance of the oxide film having air pores is as high as that of vacuum. As a result, an ideal insulation film can be obtained.
When the sol-gel method is applied to a real production line, a coating unit that coats a coating solution to a wafer, an aging unit that contacts ammonium gas to the wafer or heats the wafer at a predetermined temperature (for example, around 100.degree. C.) and gelatinizes the coated film, and a substituting unit that substitutes the solvent of the coated film with another solvent are required.
In the gelatinizing treatment performed by the inventor of the present invention, as shown in FIG. 10, a wafer W is placed on a plate 61. A cylindrical lid 62 is placed on the plate 61. Thus, a sealing vessel 6 is formed. Ammonium gas is supplied from a gas supplying path 63 on the periphery of the plate 61. The ammonium gas is exhausted from an exhausting path 64 at the center of the lid 62.